Mambele Sickle Sword

[RobertGuy]

Up for view and comments is what I believe to be a Mambeli Sickle Sword from the Northern Congo. I have also seen these described as Mambele, so not sure which is right or if the spellings are interchangeable.

Description:
Single-edged extremely curved sword with double-edged portion to the tip. Blade is sharpened on the inner surface of the curve. Wooden handle wrapped in copper strip. Some crude line detailing near the hilt and at the point where double-edged blade begins. Decorated hole at the rear of double-edged portion. Cresent shaped protrusion near hilt which is for a strap to be attached. (new strap in place)

Stats:
Weight: 1lb 2oz (0.51kg)
Length overall: 30'' (76cm) Blade: 26.5'' (67cm) Measured from tip across the arc of the blade. 8'' (20.5 cm) double edged portion.
POB: 10.5'' (27cm) from hilt
Profile taper 1.11'' (28.3.3mm) for most of the blade, 1.96'' (50mm)at the start of the double-edged portion.
Distal taper 0.2'' (5.2mm) for most of the blade. Unusual blade geometry means final 8'' is 0.16'' (4.2mm) at its thickest.

I have seen reports that these blades ( or some examples thereof) may be iron rather than steel. Is there any way of checking apart from bending the blade to see how easily it takes a set? I have mentioned the unusual blade profile and have tried to illustrate it by the diagram. This blade is anything but a nice lenticular cross section. Does any body know the purpose of the hole in the blade? Decoration?, for a hanging hook?, ceremonial?, steel termites?
As ever all comments and information welcomed.